Operating Instructions MI 34 / MI 34 H
GEBAmi34e.11a.docx
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Figure 17 The middle ear
hearing
nerve
ear canal
middle
ear
bones
ear drum
middle ear
eustachian tube
cochlea
musculus
stapedius
Figure 18 Ipsilateral test
Figure 19 Contra lateral test
6. How to measure the Stapedius reflex
6.1 The basics of the Stapedius reflex measurement
While the Tympanometry method measures the change of the compliance
caused by changing pressure in the outer auditory canal, the Stapedius
reflex measurement works with a changing compliance caused by
contraction of the Stapedius muscle in the middle ear. The contraction -
called Stapedius reflex - causes a decrease in compliance and is caused by
loud acoustic stimuli.
Regardless whether the
acoustic stimulus is active
on the left or on the right
or on both sides the
Stapedius reflex is always
binaural, i.e. it occurs in
both ears at the same
time.
The Stapedius reflex is
caused in ears of adults
with normal hearing by
sine sounds with sound
pressure levels between 70
and 105 dB.
The reflex method measures continuously in one ear, the “probe ear”, the
compliance with the pressure which caused before the highest compliance.
Simultaneously the “stimulus ear” is irritated by the sound which causes
the contraction of the Stapedius muscle.
The ipsilateral reflex measurement uses the same
ear for the probe and the stimulus. The contra-
lateral measurement uses different ears for the
probe and the stimulus. The acoustic stimulus is
offered to the ear opposite to the “probe ear”.
If the offered stimulus causes a reflex the
impedance measuring instrument registers a
decrease in compliance in the “probe ear” which
indicates a Stapedius reflex at the actual test
frequency and the test level. The test level which